MILITARY strategists
have dreamed for years of being able to stop an incoming missile
in midair. Missile interception was the goal of the Strategic Defense
Initiative of the 1980s and is a Department of Defense (DoD) goal
today.DoD
has hired the Boeing Corporation as the lead system integrator for
a weapons system to intercept an incoming ballistic missile. Boeings
interceptor for the Ground-Based Mid-Course Defense (GMD) program
is currently being flight tested.For
the flight tests, a missile loaded with a kill vehicle
is launched from Reagan Test Range at Kwajalein Atoll in the Pacific
Ocean, to target the mock weapon-laden reentry vehicle of a missile
launched from Vandenberg Air Force Base in California. Under contract
to Boeing, a Livermore project has developed several sensors whose
data help DoD determine whether the interceptor met the goal of
killing the target missile. Physicist
Alex Pertica leads Livermores Remote Optical Characterization
Sensor Suite (ROCSS) project. Some of the ROCSS instrumentation
has been developed by the Laboratory, and some is available commercially.
Spectrometers examine the chemical makeup of the debris from the
midair intercept while radiometers measure impact temperature and
intensity. At the same time, high-speed cameras document the intercept
event. Livermore
is one of several research organizations and companies responsible
for monitoring the flight test program. Our niche, says
Pertica, is the collection of spectral information as well
as high-speed video to reveal the phenomenology of the intercept.
Other organizations are tracking debris fragments and providing
additional photo documentation of the intercept.

A tracking mirror (right)
points out of a window of the high-altitude observatory (HALO)
jet. The window is designed to admit infrared light for several
of the onboard sensors. On the left is the front end of Livermores
instrumentation, whose fiber-optic lines carry data to individual
sensors.

High-Flying
Instruments Livermores sensors
and camerasas well as the instrumentation of other organizationsfly
in a retrofitted business jet known as a high-altitude observatory
(HALO). HALO flies at an altitude of about 14 kilometers, high above
the weather. At least one Lawrence Livermore scientist is onboard
each flight and must take Air Force high-altitude training before
flying.The HALO takes off from Reagan
Test Range about 1 hour prior to the launch of the target missile
from Vandenberg. Once in the air, HALO remains within 650 to 900
kilometers of the interceptor missile, also launched from Reagan
Test Range, until the intercept occurs. A tracking mirror onboard
the jet is guided by ground-based radar and tracks the trajectory
of the interceptor missile.The jets high altitude
not only keeps it above the weather but also provides for increased
atmospheric transmission of infrared light. Many onboard sensors,
including several of Livermores, collect data in the infrared
wavelengths. The ROCSS telescopes collect light through a window
specially designed to transmit infrared light and channel it to
the instruments via fiber-optic lines.Five Livermore instruments
fly onboard the HALO to collect data on the final boost of the interceptor
rocket and then on the kill vehicles collision with the reentry
vehicle. A highly sensitive infrared echelle-grating spectrometer
(EGS) detects the presence of gaseous chemical species in the effluent
cloud. This instrument was developed at Livermore for another purpose
entirely: to sniff the smokestacks of suspected chemical
and nuclear facilities for tell-tale traces of weapon production.Another spectrometer operating
in the visible wavelengths estimates temperatures and identifies
materials produced by the interceptors boost phase and by
the collision of the interceptor with the target missile. It provides
especially useful data about the first instant of the hit, just
as the two vehicles are beginning to touch. A short-lived flash
at that moment reveals the signatures of the metals that are crashing
together.Radiometers operating in
the visible, short-wavelength infrared, and mid-wavelength infrared
spectral bands collect data on the temperature and intensity of
the boost and the impact. A high-speed camera that captures 16,000
frames in 4 seconds records the evolution of the debris cloud created
by the collision. A slower-speed videorecorder and another analog
video system also record the collision.

(a) The timeline shows events
for the interceptor missile fired from Kwajalein in seconds
after launch of the target missile (TALO) from Vandenberg Air
Force Base. (b) During the boost of the interceptor rocket,
the spectra for hydrogen chloride (HCl) are visible as the rocket
comes into view, although light in the blue wavelengths is attenuated
by atmospheric absorption. (c) Thirty-seven seconds later, with
less atmospheric attenuation, HCl begins to dominate the spectrum.
(d) Eleven seconds later, the practiced eye can see atmospheric
methane absorption and a dense cloud of alumina particles from
the rockets exhaust. (e) Finally, as the missile turns,
HCl again dominates the spectrum.

Getting
to the First Test FlightThe
EGS was first applied to ballistic missile defense in September
1998. On the ground at the White Sands Proving Ground in New Mexico,
the EGS successfully detected the exhaust chemicals from an Army
Theater High Altitude Area Defense (THAAD) rocket. The chemicals
it detected, primarily hydrogen chloride, almost exactly matched
the model for the rockets exhaust materials. We were
quite pleased with that first test, says Pertica.Numerous other tests from
1999 to 2001 were equally successful. One took place in Livermores
High Explosives Application Facility with an explosion designed
to simulate an intercept. In June 2001, Livermores ROCSS instrumentation
was integrated into the HALO jet. In the first flight of the ROCSS
instrumentation, HALO followed a rocket launched from Vandenberg
Air Force Base to detect chemical effluents in the rockets
exhaust. In a similar test, the jet trailed an Atlas 3B rocket launched
from Kennedy Space Center in Florida.The first actual intercept
test for ROCSS was Intercept Flight Test 8 (IFT-8) at Kwajalein
in March 2002. During an 80-second period, from 1,308 to 1,388 seconds
after launch of the target missile, the EGS data reveal first hydrogen
chloride in the rockets emissions as the interceptor comes
into view, then increased hydrogen chloride as atmospheric attenuation
lessens, and later, hydrogen chloride mixed with atmospheric methane
and a dense exhaust of alumina particles. (See the figure above.)
In the final spectrum, the hydrogen chloride is clear again as the
interceptor turns to expose its engine.This spectral information
can also indicate temperatures of the exhaust using the line intensities
from the two isotopes of hydrogen chloride: hydrogen chloride-35
and hydrogen chloride-37. If the intercept involves an enemy missile,
chemical and temperature data can be used as a diagnostic tool to
determine the type incoming rocket.Also, adds Pertica,
if a rocket isnt performing as expected, temperature
information is especially useful for indicating possible problems.Images from the high-speed
camera during the intercept reveal the growth of what Pertica calls
a worm of debris. The worm begins its growth at the first instant
of the kill vehicles collision with the ballistic missiles
reentry vehicle and continues to develop until the debris cloud
dissipates.

The high-speed camera captures
16,000 frames in 4 seconds from the moment that the kill vehicle
collides with the reentry vehicle. The development of the worm
of debris from the collision is shown in these two frames.

What
Lies AheadWith
that first flight test, Livermore completed the development phase
of this project. The next phase is deployment, which is planned
to continue through 2008 and IFT-26. The next flight test, IFT-9,
is scheduled for late in 2002.The
ROCSS team plans to upgrade the EGS to include the full mid-wavelength
infrared range, almost doubling its spectral coverage. This spectrometer
and other ROCSS instrumentation may begin supporting future development
tests of the new GMD booster, in addition to the intercept flight
tests.Pertica hopes to develop
a broader capability for monitoring intercepts with instrumentation
mounted either on satellites or flying along on the kill vehicles
booster rocket, paving the way for eventual kill assessment of intercepts
from real enemy missiles.Katie
Walter